A rib or rectangle-like optical waveguide, where an optical waveguide core is formed of a high refractive material and where an optical waveguide clad is formed of a low refractive material between two or more kinds of materials with different refractive indices, has been regarded as a promising technology applied to an optical integrated circuit by a Planer Light Circuit (PLC).
In particular, in an optical waveguide device using a material system having a high refractive index difference, generally, a strong light confinement effect by a photonic band gap can be expected in a light wavelength order of 0.3 μm to 0.7 μm, and applications to various optical elements or micro optical circuits using the same are also expected.
As a conventional waveguide type polarization splitting element, Japanese Laid-Open Patent Publication HEI 9-236718 discloses a construction composed of a single mode type first optical waveguide formed to have a double refractive property, and a single mode type second optical waveguide formed such that its propagation constant is almost equivalent to the propagation constant of a one-side polarization component of the first optical waveguide.